Numerical analysis of magnesium to aluminum joints in friction stir blind riveting

Friction stir blind riveting (FSBR) is a new dissimilar material joining method that takes advantage of both friction stir welding and mechanical blind riveting. However, no research has been conducted to investigate the stirring effects on energy transformation, material flow and temperature evolution in FSBR, which are critical to help understand the FSBR process. This paper described a hybrid numerical model integrating both finite element method (FEM) and smooth particle hydrodynamics(SPH) approach to predict the stirring effects in FSBR lap joint of Mg/Al. In this SPH-FEM model, only rivet plunging process was simulated, and the following mandrel pulling process was not considered. The Johnson-Cook equation was used to describe the constitutive material properties. The model was validated by comparing thrust forces and torques from numerical prediction and experimental results. From the simulation, it was found that (1) the main input energy was consumed by the torque to generate interfacial friction heat and the heat generated from workpiece deformation was negligible; (2) the maximum welding temperature in Mg (~620 ^o C) was higher than that in Al (~590 ^o C), and both maximum temperatures are close to the melting points; and (3) the evolution of material flow illustrated the formation process of interlocking between Mg and Al.